P17.35.B SAFETY AND FEASIBILITY OF YTTRIUM-90 GLASS MICROSPHERES IN RECURRENT GLIOBLASTOMA: RESULTS FROM THE FIRST 12 PATIENTS TREATED IN THE FRONTIER TRIAL

Abstract BACKGROUND Glioblastoma (GBM) is highly aggressive with poor prognosis, especially in recurrent cases where treatments are limited. Intra-arterial (IA) Yttrium-90 (Y90) microsphere therapy, CE-marked for hepatic neoplasia, offers the potential for targeted high-dose beta radiation in GBM by leveraging tumor hypervascularity. The FRONTIER trial evaluated the safety and feasibility of IA Y90-glass microsphere treatment for recurrent GBM. MATERIAL AND METHODS FRONTIER is a prospective, single-arm, multi-center study with Investigational Device Exemption approval from the US FDA. This initial cohort included patients with recurrent GBM in non-dominant, non-eloquent regions after 1-2 lines of prior therapy. The primary endpoint was the 30-day incidence of treatment-related toxicities (primarily ≥grade 3 non-hematologic, with exclusions). Secondary endpoints included overall treatment-related adverse events (AE), neurological function changes, technical success, and efficacy measures. Treatment regions, defined via cerebral angiography-MRI fusion to cover the recurrent lesion were targeted with 40±4Gy. Post-treatment evaluations included MRI, Y90-PET for absorbed dose distribution, and serial neurological assessments. Changes in post-contrast T1-enhancing tissue volume (T1C-vol) were tracked longitudinally. RESULTS Twelve subjects (67% male; average age 57 years) were treated. The procedure was well-tolerated with no limiting toxicities reported or device-related AEs reported. Five patients experienced 8 procedure-related AEs (6 Grade 1, 2 Grade 3). At discharge one day after treatment, there was no decline in neurologic status per NIHSS. Technical success was 100%, with post-treatment Y90-PET showing a median absorbed dose of 41.5 Gy (range 39.2-45.4) to the treatment region (median volume 80.3 cc [40.9-118.5]). The median tumor absorbed dose was significantly higher at 124.2 Gy (range 58.5-508.5) within a median tumor volume of 5.8 cc (range 0.5-55.4), indicating preferential tumor perfusion. At 1 month, the best response was partial response in 17% (2/12), stable disease (SD) in 67% (8/12), and progressive disease in 17% (2/12). At 2 months, 73% (8/11 evaluable) had SD, and 33% (4/12) showed reduced T1C-vol within the treated area. Median progression-free survival was 3.0 (95% CI 1.1-3.7) and median overall survival (OS) was 9.3 months (95% CI 5.0-NE) from Y90 treatment. Exploratory analysis revealed a significant OS benefit for patients receiving a tumor absorbed dose above the median (>124 Gy) compared to those below (13.1 vs 5.8 months, p=0.0054). CONCLUSION Results from this initial cohort of the FRONTIER trial suggest IA Y90 glass microsphere therapy is technically feasible and well-tolerated in patients with recurrent GBM. The observed dose-response relationship warrants further investigation of this modality as a potential treatment option.